Dispensing devices are generally well known in the art. Note, for example, the patent to Moeller, U.S. Pat. No. 2,884,165 and the patent to Kishner, U.S. Pat. No. 3,679,331. In the Moeller patent a deformable tube is filled with a material to be dispensed. The tube is then pinched off from a source of supply and a movable platen is used to deform the tube and dispense the material. The length of stroke of the platen is controlled to regulate the amount of material to be ejected from the deformed tube.
In the patent to Kushner several differently sized deformable tubes are provided with fluid. Fluid in the tubes is dispensed by deforming the tubes with a plate actuated by a cam. Other dispensing apparatuses are described such as in the patents to Maclin, U.S. Pat. No. 3,684,408 and Allen et al., U.S. Pat. No. 3,308,898 with the latter describing use of a deformable tube to dispense a granular material.
The use of deformable tubes for dispensing material is particularly advantageous to prevent contamination and corrosive effects. It is desirable that deformable tubes dispense material in a constant manner. This is particularly important when small amounts are to be repetitively discharged.
The types of materials which may be dispensed can have a wide range of viscosities. The accuracy of the amount dispensed in some cases will tend to vary with viscosity. For example, when a low viscosity material is to be dispensed through a deformable tube in a highly precise manner, accurate control over the amount of deformation of the tube must also be maintained while the material is flowing.
A deformable tube metering valve generally relies upon the natural resilience of the tube material to provide the force needed to restore the tube to its natural state. However, certain materials may include adhesive characteristics which inhibit the restoration of the tube opening and thus impede the flow of material through the tube resulting in inaccuracies in the dispensation. In other instances an over-pinching of the deformable tube may result in impeding a restoration of the normal shape of the tube.
A conventional deformable tube has a cylindrical shape which is pinched in an area to restrict the tube opening. The pinching increases wall stresses, particularly when a complete tube restriction is needed to terminate flow of a low viscosity material. The wall stresses often lead to tube deterioration from fatigue when pinching takes place at the same place for repeated dispenser actuations. The result can be a perceptible drift in the accuracy of the material being dispensed and a subsequent loss of control over the process in which the deformable tube metering valve is employed.